Disclosed are methods and apparatus for controlling a level of a marking material in a waste sump. The apparatus may be a printing apparatus.
The basic principles of electrostatographic printing with dry marking material generally referred to as xerography) are well known: an electrostatic latent image is created on a charge-retentive surface, such as a photoreceptor or other charge receptor, and the latent image is developed by exposing it to a supply of toner particles, which are attracted as needed to appropriately-charged areas of the latent image. The toner particles are then transferred in imagewise fashion from the photoreceptor to a print sheet, the print sheet being subsequently heated to permanently fuse the toner particles thereto to form a durable image.
Following the transfer of the image from the photoreceptor to the print sheet, residual toner particles remaining on the photoreceptor are removed by any number of known means, such as a cleaning blade, brush, and/or vacuum. In a typical embodiment, the removed toner is accumulated in a hopper. Accumulated waste toner is directed, typically by an auger, into a waste container.
The toner acts as a lubricant between the photoreceptor and the cleaning blade. If there is not enough toner left on the photoreceptor after transfer of the image to the print sheet, there may be increased wear on the photoreceptor and/or the cleaning blade, which could result in premature failure. There are many potential causes that can lead to the condition of not enough toner on the photoreceptor after transfer of the image to the print sheet. Many of these causes are customer driven & machine environment driven (for example: extended low area coverage print jobs in one or more colors; or temperature, humidity, altitude). Any other variability, such as manufacturing variability or design change variability, that causes a xerographic setpoint, such as developed toner mass or toner transfer efficiency, can also cause the condition of not enough toner on the photoreceptor after transfer of the image to the print sheet. This condition may result in insufficient toner left on the photoreceptor to act as an effective lubricant.